(1) Field of the Invention
The present invention relates to a seat belt retractor for use in a safety seat belt system of a motor vehicle. More particularly, this invention relates to a seat belt retractor having provisions for rewinding or resetting a spring which is specifically adapted to take up a slack in the seat belt in an emergency situation.
(2) Description of the Related Art
It is well known to use a three-point safety seat belt system to safeguard the occupant of a vehicle seat by restraining the body of the occupant in an emergency situation. Generally, one end of the seat belt is attached to a first securing point anchored to a vehicle floor or a seat itself at a side of the seat. A second securing point, composed of a tongue plate and buckle assembly, is provided at the other side of the seat to form between the first and second points a lap belt section of the seat belt for restraining the lower torso of the occupant. A third securing point, which is in the form of a slip ring attached to a door pillar or a belt-pull-out slot provided at the top of a backrest of the seat, is provided at the same side of and above the first point to form a shoulder belt section diagonally and upwardly extending from the second point to secure the upper torso of the occupant. The other end of the seat belt is finally attached in a retractable manner to a retracting reel of a seat belt retractor which is located on the door pillar or housed within the seat backrest.
In order to avoid imparting unnecessary constraint to the occupant during non-emergency conditions, there has been widely used the so-called emergency-locking-type retractors (ELR) having an inertia responsive latch mechanism. An ELR is designed to retract the seat belt with a relatively small winding force by biasing the retracting reel with a spiral spring having a small torque or spring force. This prevents the seat belt from being fit too tightly around the user and permits the seat belt to be protracted upon application of a small tension thereby affording flexibility of movement to the occupant. In an emergency condition, an inertia sensing element senses sudden deceleration of the vehicle and actuates the latch mechanism to lock the retracting reel, thereby preventing further protraction of the seat belt and preventing the occupant from being thrust forward.
The use of ELR, however, tends to result in some slack in the seat belt. Such slack is unnecessary in emergency situations. Thus, it has been proposed in the art to improve the ELR such that, in an emergency situation, the seat belt is instantaneously tightened to remove slack (Japanese Unexamined Utility Model Publication (Kokai) No. 58-67461, published May 7, 1983). Toward this end, the retractor is provided with a second slack-take-up spring having a stronger spring force than the first retracting spring and connected to a drive shaft mounted rotatably on the retractor body. The drive shaft is coupled with the retracting reel through a one-way clutch which is engaged and disengaged by a trigger mechanism having another inertia sensing element. The slack-take-up spring has been preliminarily wound to bulid up spring energy therein required to turn the retracting reel through, for example, one revolution. In the emergency condition, the trigger mechanism releases the spring energy stored in the slack-take-up spring and engages the one-way clutch so that the rotational torque applied by the slack-take-up spring to the drive shaft is transmitted to the retracting reel causing it to turn through about one revolution, thereby removing the slack and tightly fastening the belt around the occupant.
This retractor, however, has the disadvantage that, once the spring energy of the slack-take-up spring is released in an emergency situation, the retractor must be removed from the automobile and the drive shaft must be turned by a tool such as a wrench or screwdriver to rewind or reset the slack-take-up spring to restore the spring energy for a subsequent emergency situation.